Ball and socket joints are used in many areas of mechanical engineering and especially in automotive engineering as components of chassis and steering assembly units. The bearing shells present in the ball and socket joints surround a so-called ball head as a component of a ball and socket joint pivot and are in turn mounted in a ball and socket joint housing. The ball and socket joint pivot and the ball and socket joint housing are arranged, on the one hand, on the chassis side or the steering side and, on the other hand, they are fixed to the body, so that motions of both components in relation to one another are made possible in certain defined degrees of freedom. The general problem in connection with the mounting of the ball and socket joints is that the bearing shell must surround the ball head located therein by more than half for securely holding the ball pivot in order to avoid an unintended separation of the bearing shell from the ball pivot. Due to the fact that the ball pivot is surrounded by the bearing shell by more than half, it is not possible to easily put together the two components. The bearing shell must rather be designed by a special design in terms of shape and/or material technology such that it can be pulled over the ball head during the mounting process and can be fixed based on its elastic properties or other design specifications in connection with the subsequent installation of the bearing shell in the ball and socket joint housing.
Two different design variants are known, for example, from DE 199 58 149 A1 for solving the problem.
On the one hand, the bearing shell may be provided with a plurality of longitudinal slots. The bearing shell itself is designed in this case such that it has essentially a hollow spherically shaped recess for receiving the ball head of the ball and socket joint pivot. This pivot is pressed into the recess through an existing introduction opening, and the area provided with the opening stretches towards the outside due to the slotted shape of the bearing shell to the extent that the ball pivot can be introduced.
Another variant of assembly arises corresponding to the document cited above from the fact that the bearing shell comprises two shell parts, which together form an inner, hollow spherically shaped bearing surface and which are connected to one another by means of a so-called film hinge and can thus be folded up for the mounting operation on the ball and socket joint pivot. After the attachment, the two shell parts are closed and again inserted into the ball and socket joint housing.
Both design variants have proved to be definitively useful for certain intended uses. However, the first embodiment, in which the bearing shell is provided with longitudinal slots, has the problem that the ball and socket joints used are usually exposed to a principal direction of load in the installed state. The forces occurring in the principal direction of load bring about high surface pressures within the bearing shell, and the slots in the bearing shell, which are necessary for the mounting, have a disadvantageous effect, because the plastic material is weakened and the remaining portions of bearing surface are subject to a correspondingly high stress. Under unfavorable operating conditions, this may cause the plastic material of the bearing shell to become subject to creep or flow motion, which means that the size of the slots will irreversibly decrease, which leads to a reduction or elimination of the prestress necessary for the absence of clearance in the ball and socket joint.
To avoid such drawbacks, the above-mentioned second design variant, in which a film hinge connects two shell parts to one another and makes it possible to fold up the bearing shell for mounting purposes, is used for certain applications.
However, it is disadvantageous in this case that only stretchable plastic materials can be used for such bearing shells, because up to 50% stretchability of the material is necessary for the film hinge to function. Plastics such as polypropylene or polyethylene are therefore used, as a rule, for such bearing shells. However, these materials lack sufficient loadability for certain applications of ball and socket joints, so that the size of the ball and socket joint may have to be increased to absorb the forces occurring.